Blue Stains on Tile


Nick Valenti

 January 7, 2019. 4:36 PM

Are the tiles in your bath, shower, shower head or faucets, turning blue? What causes this discoloration and where does it come from? In most cases, blue/green tinted stains are caused by the water flowing through your pipes having a low (acidic) pH. Chances are your water pipes are made of copper and the blue discoloration is the result of the insides of the pipes being attacked by the aggressive low pH water.


To better understand, pH is the measure of acidity in water. Below is the pH scale which ranges from 0 to 14, with 7 being absolute neutral. Any measurement below 7 is acidic, any measurement above 7 is alkaline. If the pH of your water is 6.8, it is considered “aggressive” and can damage metal pipes, faucets and fixtures. Blue stains begin to appear when the pH of the water is 6.8. To further add insult to injury, each 0.10 of a point is exponentially more aggressive than the number before it. Determining pH can be done by simply performing an on-site pH test, which can be purchased from most local hardware stores or online.

Water Hardness Table of Classifications
grains per gallon (gpg) milligrams per liter (mg/L) parts per million (ppm) U.S. Geological Survey Classification Water Quality Association Classification
< 1.0 < 17.1 soft soft
1 to 3.5 17.1 to 60 soft slightly hard
3.5 to 7.0 60 - 120 moderately hard moderately hard
7.0 to 10.5 120 - 180 hard hard
10.5 + 180 and over very hard very hard

For instance, if your water tests show a pH of 6.5, you may not be too alarmed because it’s only a few points away from 6.8. Right? Unfortunately, this is a big mistake. Water with a measured pH of 6.5 can cause considerable damage over time, eventually causing serious problems with metal plumbing in your home, and other household appliances, like water heaters, dish washers and ice makers.

Although acidic pH water is the most common cause of blue tiles, the opposite effect, or too much alkalinity, can also have damaging effects, such as clogged pipes and fixtures, or slow running faucets. Blue stains can be removed from tiles but only temporarily, unless the source cause is determined and repaired.


Removing the Stains

To remove blue stains from tile, we recommend applying a heavy-duty cleaner specifically designed to remove cleanly without damaging your surrounding tile. Performing a small spot-check on an inconspicuous area of the tile is also a good Idea.

For cleaning blue stains from shower/bathroom tiles, we suggest applying MAPEI's UltraCare Heavy-Duty Stone, Tile & Grout Cleaner mixed with equal parts water for cleaning the tiles. Apply the solution to the affected area and allow it to stand for 5-10 minutes. Once complete, apply UltraCare Abrasive Surface Cleaner directly onto the same area and scrub using a white scrub pad. Rinse with clean water and dry with a clean towel.

Products mentioned in the article

UltraCare Abrasive Surface Cleaner
UltraCare Abrasive Surface Cleaner
Abrasive Surface Cleaner UltraCare Abrasive Surface Cleaner is a powerful, abrasive cleaner that is safe for use on a variety of ceramic,…
UltraCare Heavy-Duty Stone, Tile & Grout Cleaner
UltraCare Heavy-Duty Stone, Tile & Grout Cleaner
UltraCare Heavy-Duty Stone, Tile & Grout Cleaner is a highly concentrated and high-alkaline cleaner and degreaser. This product is…


Nick Valenti

Nick Valenti

Nick joined MAPEI in 2012 as the technical expert for the UltraCare line. He has more than 25 years of experience in the sealers and cleaners product line. While his experience includes an in-depth knowledge of products, Nick also understands the major issues and problems that can arise with the surfaces to be protected and has solutions for these challenges. In charge of training MAPEI’s Sales and Technical Service teams, Nick is even more importantly the in-the-field resource for MAPEI’s customers and end users.


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